Hibernate Transformers之三种结果转换说明

在hibernate使用的过程中.我们通常需要对结果进行解释. 
Hibernate为我们提供了以下3种解释方法: 

Transformers.ALIAS_TO_ENTITY_MAP //把输出结果转换成map
Transformers.TO_LIST //把结果按顺序排进List
ransformers.aliasToBean(target) //把结果通过setter方法注入到指定的对像属性中

在Hibernate中Transformers的所有转换都是需要实现ResultTransformer接口 

详解ALIAS_TO_ENTITY_MAP ,太简单了就是把key和值直接转换到Map当中 

public Object transformTuple(Object[] tuple, String[] aliases) {
        Map result = new HashMap(tuple.length);
        for ( int i=0; i<tuple.length; i++ ) {
            String alias = aliases[i];
            if ( alias!=null ) {
                result.put( alias, tuple[i] );
            }
        }
        return result;
    }

详解TO_LIST,转换过程很简单,就是把value转换成List对像 

public Object transformTuple(Object[] tuple, String[] aliases) {
    return Arrays.asList( tuple );
}

详解aliasToBean,转换过程就是通过读取查询后的字段.然后通过使用setter方法注入到目标对像中 

public AliasToBeanResultTransformer(Class resultClass) {
        if ( resultClass == null ) {
            throw new IllegalArgumentException( "resultClass cannot be null" );
        }
        this.resultClass = resultClass;
        //定义属性访问器.
        propertyAccessor = new ChainedPropertyAccessor(
                new PropertyAccessor[] {
                        PropertyAccessorFactory.getPropertyAccessor( resultClass, null ),
                        PropertyAccessorFactory.getPropertyAccessor( "field" )
                }
        );
    }

    public Object transformTuple(Object[] tuple, String[] aliases) {
        Object result;

        try {
            if ( setters == null ) {
                setters = new Setter[aliases.length];
                for ( int i = 0; i < aliases.length; i++ ) {
                    String alias = aliases[i];
                    if ( alias != null ) {
                        //初始指定的setter方法
                        setters[i] = propertyAccessor.getSetter( resultClass, alias );
                    }
                }
            }
            //实例实体对像
            result = resultClass.newInstance();

            for ( int i = 0; i < aliases.length; i++ ) {
                if ( setters[i] != null ) {
                    //向setter方法中指定的属性注入值
                    setters[i].set( result, tuple[i], null );
                }
            }
        }
        catch ( InstantiationException e ) {
            throw new HibernateException( "Could not instantiate resultclass: " + resultClass.getName() );
        }
        catch ( IllegalAccessException e ) {
            throw new HibernateException( "Could not instantiate resultclass: " + resultClass.getName() );
        }

        return result;
    }